(1) Field of the Invention
The present invention relates to a method of controlling an exothermic reaction, using water, of an exothermic composition, the exothermic composition, an exothermic device and an application pad. More particularly, the invention relates to an exothermic reaction of an exothermic composition, the exothermic composition, an exothermic device and an application pad, in which the exothermic reaction is controlled so that an exothermic temperature is maintained below a predetermined temperature to enhance safety when applied to a living body such as a human body.
(2) Description of the Related Art
In recent years, hot compresses and body warmers have been employed which utilize, as a heat source, the heat of a reaction with oxygen in the air of an exothermic composition containing a metal powder, a metallic chloride and water as essential components thereof. One familiar example is a disposable body warmer in which an exothermic composition including a metal powder, a metallic chloride, water, a catalyst and an exothermic auxiliary is enclosed in a flat pouch gas-permeable in one or both surfaces thereof.
Some disposable body warmers have an adhesive layer formed on one surface thereof to be pasted directly or through underwear to the skin. Where this type of body warmer is used as a hot compress, the adhesive layer may include skin absorbable medication, a far infrared radiator and a magnetic substance dispersed therein.
Where this type of exothermic composition is used as a body warmer or hot compress, it is necessary to generate heat of a predetermined temperature, e.g. 37.degree. C. or above, higher than the average body temperature in order to provide a sufficient heating or therapeutic effect. On the other hand, it is desirable to control the heat below 43.degree. C. or so in order to prevent a low-temperature burn. This is because a low-temperature burn could be inflicted if a temperature exceeding 43.degree. C. were maintained for a long time.
In an initial attempt to control the exothermic temperature of the exothermic composition, the gas permeability of the pouch was controlled to control the quantity of air (quantity of oxygen) taking part in the reaction. With this method, water vapor is produced inside the pouch in an increasing quantity with a temperature increase resulting from the exothermic reaction. The water vapor adheres to pores of the pouch to vary its permeability. It is therefore difficult to control the permeability in a steady manner.
That is, water vapor adheres in varied quantities to the pores of the pouch having the same permeability, depending on the type of the pouch, e.g. pouch materials, filling agents, or whether a surface activating treatment has been given or not. Thus, it has been impossible to obtain an exothermic device of reliable quality.
A method proposed subsequently of controlling the heat of the exothermic composition consisted in controlling the water-vapor permeability of the pouch. Compared with controlling the exothermic temperature of the exothermic composition by means of gas permeability, this method realizes a strict temperature control, to provide an exothermic device assuring increased safety.
In order to secure both heating or therapeutic effect and safety, a gas-permeable film used has a water-vapor permeability specified by the ASTM method (E-96-80D method), with a narrow range of variation at plus/minus 5 to 10% of the standard value, or plus/minus 20 to 35% of the standard value at most.
The flat pouch gas-permeable in one or both surfaces thereof has the one surface or both surfaces formed of a gas-permeable film. The gas-permeable film is formed by drawing a plastic film, or laminating a gas-permeable reinforcing base material such as a nonwoven fabric on the drawn plastic film.
However, in manufacturing an exothermic device, it has always been difficult to reduce the range of variation in the water-vapor permeability of a gas-permeable film as noted above. Where a material having a certain range of such variation is used, an increased number of defective gas-permeable film products are manufactured, resulting in high cost and a waste of resources.
Even when gas-permeable film products are limited to a particular range (what is known as a delivery specification) of water-vapor permeability, all of the products received are not necessarily in this range. Some of the gas-permeable products received are off-specification products. Consequently, some pouches are formed of the gas-permeable film with off-specification water-vapor permeability. The exothermic composition may have variations, and environment such as ambient temperature or humidity may be different also.
As a result, variations occur in the maximum exothermic temperature, and high temperatures exceeding a predetermined temperature cause varied harmful effects.
Specifically, in the case of an exothermic device or application pad applied to the human body, for example, varied harmful effects such as blisters, erythema or other conditions are caused through a low-temperature burn. In practice, therefore, instructions are given regarding use of the exothermic device or application pad, for example, in the form of specifying sites of application, forbidding repeated application to the same site, forbidding use of a belt or the like to press the exothermic device or application pad, or forbidding direct application to the skin. Various other instructions may be essential, such as instructions to stop use immediately when an excessive heat is felt or to avoid use during a period of sleep.
Depending on use environment for the exothermic device, particularly at a high ambient temperature, the exothermic reaction may progress at too high a rate, whereby the exothermic temperature exceeds an intended maximum exothermic temperature. This poses a disadvantage in safety enhancement.
Inventor has made intensive research in an attempt to realize an extended use period by retarding the exothermic reaction to lower the exothermic temperature when the exothermic temperature exceeds an intended maximum exothermic temperature, and by suppressing an excessive exothermic reaction of the exothermic composition.
It has been found as a result that the heating principle of a disposable body warmer and the like is based on a heat generation occurring with the oxidation of a metal powder, and the rate of this oxidation, or exothermic reaction, is greatly influenced by the quantity of water in particular.
That is, to promote this oxidation, an appropriate degree of moisture is the key; the reaction is markedly retarded if moisture is too much or too little. A good balance between necessary moisture and air (oxygen) supply is said to maximize the rate of oxidation or exothermic reaction.
Too little moisture results in a shortage of moisture necessary for the reaction though air is sufficient. Too much moisture results in barrier layers of moisture to diminish air supply, thereby retarding the reaction.
Inventor has found that, where the exothermic composition includes a water absorber which, at above a predetermined temperature, releases adsorbed water to increase free moisture, and the free moisture forms barrier layers to diminish air supply and lower the exothermic temperature. With lowering of the exothermic temperature, the water absorber adsorbs the free moisture to eliminate the barrier layers, thereby increasing air supply. Thus, it has been found, the exothermic temperature maintains a certain value or rises and falls between a certain maximum temperature and minimum temperature, which has led to completion of the present invention.